A Study On Regional Evaportranspiration Model Based On Remote Sensing Method And Its Application In The West Jilin Province

"The development of China depends on Northeast China. The rehabilitation of Northeast China relies on Jilin Province. And West Jilin Province is the key to the booming hope of the province as a whole. However, the problem of ecological environment restricts the development of the west. And water resource plays a critical role in the problem."The summary is the true picture of the bottle-neck which undermines the breakthrough of social and economic development of Jilin Province. Therefore, it is a significant importance that we explore the ecological environment problem in west Jilin province from the point of view of water balance. The land surface evapotranspiration is the important component of energy balance and the primary portion of water balance. It is not only important to the study on global climate evolvement, entironment and the assessment of water resources, but also is vital to guide the drainage and irrigation set-up, monitor droughts and improve water resource use efficiency. In essence, the issue of eco-environment is the problem of water resource. Water balance is the threshold of studying eco-environment. Thus we must investigate thoroughly the relationship between the regional evapotranspiration and the entironment change. It is hopeful that this study will provide valuable ideas in the restoration and reconstruction of the eco-environment for the west Jilin province. Grassland degradation, land salinization and soil desertification are typical environmental problems in Western Jilin province. It is an urgent task to find out the mechanism and drive forces that cause the deterioration of eco-environment and searching for approaches for restoring the eco-environment system in the region. The study emphasizes on the establishment of the region remote sensing model of evapotranspiration, the land use change model in time and space, the temporal and spatial analysis of land surface evapotranspiration in the region and the overlay analysis between evapotranspiration data and land use data. Firstly, the paper elaborates the study purpose and signification of regional remote sensing model of evapotranspiratio, the current status and development trend of the study, the eco-environment situation in the area and the characteristic of quantitative remote sensing in eco-environment study. Secondly, land use/cover change in the study area and its impact on eco-environment are discussed. Thirdly, based on surface energy balance theory, the regional remote sensing model of evapotranspiration is constructed, and evapotranspiration data are derived from NOAA/AVHRR data. The relationship between temporal and spatial distribution of evapotranspiration and grassland degradation, land salinization and soil desertification in the area is explored through the analysis of the temporal and spatial distribution characteristics of evapotranspiration over a number of years and the overlay analysis between evapotranspiration data and land use data. Finally, the effective measures and logical advice for the restoration and reconstruction of the eco-environment in the study area are put forward from the point of view of water balance. The advice is important to the sustainable development of the west Jilin province both socially and economically. Based on surface energy balance theory, the regional remote sensing model of evapotranspiration is constructed. And Interactive data language (IDL) is chosen to implement the model algorithms. Meanwhile for the purpose of this study, the tool box of the software widely used for remote sensing image processing, named The Environment for Visualizing Images—ENVI is extended. It can be used to extract the surface physical parameter and the surface energy flux and calculate evapotranspiration in the area with NOAA/AVHRR data. At the same time, the temporal and spatial evolvement process of land use in the area is discussed in detail using land use change model. Thus the basic status of land use/cover change is clearly knowen, especially grassland degradation, land salinization and soil desertification. Using ENVI, with some specific extensions made by the author, the temporal and spatial distribution of evapotranspiration is analyzed at threetime scales, ie, year, season, and month, respectively. Then the overlay analysis between evapotranspiration data and land use data is performed. The relationship between evapotranspiration distribution and grassland degradation, land salinization and soil desertification is analyzed. And some effective measures and advice of preventing the eco-environment from degradation and restoring the environment in the area are described according to water balance. Some primary conclusions are drawn as follows: 1) The regional remote sensing model of evapotranspiration that is based on the surface energy balance equation can satisfy the precision of the regional scale, not only for the surface parameter but also for evapotranspiration. It has the extendable and referenced signification for other areas in China. 2) The results of land use modeling show that grassland degradation and land salinization in west Jilin province have been severe since 1980's. The area of sandlot reduces, but the position of soil desertification is austere from change characteristic of its space conformation index. 3) The temporal and spatial evapotranspiration distribution in the area is heterogeneous. And the annual average evapotranspiration (AAE) has a great difference. The maximum monthly average evapotranspiration (MAE) is in May, which reaches 222.9mm. The minimum is in December, which is only 37mm. The distribution of MAE forms a curve that has only one peak value. The average evapotranspiration (AE) of the second season reaches maximum, 194.4mm. The first season AE is 72.5mm. The third season AE is 163.9mm. The fourth season AE is 65.4mm. Its distribution curve is the same curve that has only one peak value as that of MAE. 4) The AAE of the east part of the study area is larger than that of the western part. The AAE of Fuyu County has the maximum value of 1607.7mm. The AAE of Songyuan City, Qianguo County, Zhenlai County and Daan County is more than 1500mm. The AAEn of Taonan County and Tongyu County is minimum, about 1406mm. The AAE of Baicheng City, Qianan County and Changling County are 1434.8mm, 1458.7mm and 1499.3mm, respectively.5) The AAE distribution curve of every county in the study area has the same shape of curve that has only one peak value. It reaches the maximum in May and the minimum in December. Its distribution status is the same as MAE of the entire area. 6) The AAE of grassland,sand land and salinization land in area increases from 1986 to 2000. The sand land AAE increases at the highest rate, the grassland follows, and the salinization land AAE has increases at a relative lower rate. It is clearly shown that evapotranspiration aggravates grassland degradation, land salinization and soil desertification in area at a certain extent. 7) To reduce evapotranspiration in the area, the efficient use of solar energy and wind energy and the growing the C4 plants that their transpiration coefficient are small and adapt to the alkaline condition are the effective step. They can solve the eco-environment problem in the area radically. Remote sensing provides an approach to monitor land surface energy and water balance over a large area simultaneously, which is very important and useful in researches and applications in global climate change, ecology, agriculture and hydrology, etc. Studies have been carried out and achieved fruitful results. This paper brings some fresh aspects. (1) The establishment of the regional remote sensing model of evapotranspiration in the west Jilin province is creative. It can satisfy precision of regional scale, and replace the general measurement method for evapotranspiration in weather stations. This may save manpower and material resources, and devote more vigor and financial to other studies. (2) It is the first time to estimate a series annual surface evapotranspiration of the west Jilin province using NOAA/AVHRR data and analyze their temporal and spatial distribution. (3) The relationship between evapotranspiration distribution and grassland degradation, land salinization and soil desertification in the study area is discussed via the overlay analysis between evapotranspiration data and land use data. And the effective measures and useful advice of preventing the eco-environment from further degrading and restoration of the environment in the area are put forward from the point of view of...